The present invention relates to thin-walled hollow bodies intended to contain one or more inserts. A typical example of such a part consists of a molded golf-club head of injectable thermoplastic material within which a mass is to be arranged. Both the weight and the position of the mass must be adjustable to optimize the function of the center of gravity and the weight of the part obtained, and thus the size and direction of the force which the player will impart to it upon its use.
French patent publication A-2 645 447 describes a golf-club head made from a molded hollow body of plastic which is open on one face. The mass which will impart the necessary inertia to the club is arranged within the cavity of the hollow body, and the body is then closed by a closure piece which is attached to it in suitable manner. This process enables production of a golf club of injected thermoplastic material having a mass which is suitable in weight and position in the club head, but the manufacture of such a club is relatively complicated and expensive.
French patent publication A-2 657 530 also proposes making a golf-club head from a closed hollow body of plastic having a filling orifice within itself which there is arranged a filling orifice which makes it possible to introduce a suitable material, for instance, being relatively expensive, this process also does not, in actual practice, permit adjustment of the weight and still less of the position of the mass within the golf-club head in a desired manner.
Another embodiment, proposed in French patent publication A-2 625 105, consists in molding the complete part in a single operation, with the volume and shape desired. Removable parts which create larger or smaller cavities within the molded part are introduced into the molded part. This process does not permit precise adjustment of the weight of the mass of the golf-club head obtained, nor precise adjustment of the function of its center of gravity.